It has been known to crush rock to produce, for example, gravel, sand, chips or the like. Manufactured sand, that is sand produced by crushing as opposed to naturally occurring sand, is often specified to be used in manufacturing cement for road construction or the like since, unlike natural sand which has been weathered and the facets worn, manufactured sand has sharp facets which provide for binding in the cement product. Hence, manufacturing sand from crushing rock is an important industry to supply sand and, for that matter, manufactured aggregate for cement.
In addition to manufacturing sand, rocks are crushed to produce gravel and rock chips for use in aggregate and cement and, for example, decorative rock gravel. In the manufacture of gravel it is important to produce a consistent and predictable crushed product such that there is a minimum of non-conforming product, e.g., sand where chips are being manufactured, which must be screened. It would be advantageous to be able to substantially select the product to be produced (whether it be sand, aggregate or chips) and crush the rocks such that a substantial portion of the crushed material falls in the range of the desired product and that a minimum of the product is lost to non-conforming output.
One approach to rock crushing is as shown in Pamplin, U.S. Pat. No. 4,257,564 which has a rotating, planar and circular crushing jaw which operates with a conical jaw. The jaws are spaced to define an annular discharge opening. The conical crushing jaw is defined, in annular fashion, about an axially disposed feed tube which supports the rotating components associated with the conical jaw. Rock is fed axially down the axial tube and the jaws rotated which feeds the rock, through centrifugal force, between the jaws where they are crushed. The lower jaw is round and flat and coacts with the conical upper jaw to define a circular nip for crushing of rock. A drawback to this type of rock crusher is that upper jaw is conical which provides an irregular, non-planar crushing face and which, it turn, increases manufacture and replacement costs of the wear surfaces. The bottom jaw is flat and as a result does not cooperate to urge rock to the nip instead relying completely upon centrifugal force. There is no technique to positively feed and direct rock between the jaws.
There is, therefore, a need for a rock crusher which overcomes the problems of prior rock crushers by, among other features and advantages, positively feeding the rocks to be crushed and which provides for less expensive construction and replacement of wear surfaces.